Method of manufacturing cathoderay tubes



' INVENT 5- Ba U nmnunnm llllllll mumu illl lifii IIII llllllmlmlll llllll J. S. BAILEY ETAL METHOD OF MANUFACTURING CATHODE-RAY TUBES Filed April 29, 1963 Jam Q5 Feb. 8, 1966 United States Patent 3,233,954 METHOD OF MANUFACTURING CATl-IQDE- RAY TUBES James S. Bailey, Chicago, and John F. De Ano, Melrose Park, Ill., assignors to The Rauland Corporation, a corporation of Illinois Filed Apr. 29, 1963, Ser. No. 276,250 5 Claims. (Cl. 316-1) This invention relates to the manufacture of cathoderay tubes, and particularly to the manufacture of such tubes which are adapted for high-voltage operation, e.g., operation with interelectrode Voltages in excess of kilovolts. The invention is particularly useful in manufacturing television picture tubes, and will be described for convenience in that connection.

A conventional television picture tube comprises a multiple electrode electron gun supported on a press which is sealed into the neck of the envelope after formation of the luminescent screen. The electron gun assembly includes a thermionic cathode, one or more anodes, and an intervening control grid for determining the instantaneous intensity of the electron beam originating at the thermionic cathode. The final anode of the electron gun is conventionally operated at voltages substantially in excess of 10 kilovolts; final anode voltages from to kilovolts are customary in present-day television picture tubes. If the tube is of the electrostatically focused variety, the gun assembly also comprises the electrostatic focusing system, and it is also quite conventional to include a getter ring as a part ofthe gun assembly.

Because of the high electrode voltages employed and the close interelectrode spacings, one of the difficulties encountered in subsequent operation has been that of intermittent arcing within the electron gun. In some instances, and especially when an arc is induced between the emissive surface of the thermionic cathode and one of the other electrodes, such arcing may lead to loss of emission from the cathode with an accompanying adverse effect on the life of the tube. Moreover, arcing in the gun structure may in some instances result in damage to the external circuit elements to which the gun electrodes are connected, as is well known in the art.

Television picture tubes have also been observed, in many instances, to produce an undesired faint glow on the phosphor screen, with an adverse effect on picture contrast, and this effect is usually attributed to cold emission, of which the major portion is generally conceded to originate from the gun electrodes or other elements constituting the gun assembly.

Both intermittent arcing and cold emission are generally attributed to the presence of lint, dust, phosphor particles, grease, or other extraneous matter on or in the gun assembly, and many precautions have been taken to assure utmost cleanliness for this reason. Measures previously taken include special rinsing baths for the gun subassemblies and the provision of hygienically clean assembly areas. However, such measures are expensive and cumbersome to employ, and arcing and cold emission have remained a major production problem.

Another measure which has been employed to reduce arcing and cold emission in finished tubes has been the so-called spot knocking procedure. In this procedure, the gun electrodes are all connected together and a high voltage, of the order of to kilovolts, is impressed between the final anode and the interconnected gun electrodes. While this voltage is applied, the neck of the envelope is tapped in an effort to loosen d-ust, lint or other foreign particles or extraneous matter which may be present in the gun structure. Some of the extraneous particles are burned out and others shaken loose by this Patented Feb. 8, 1966 "ice procedure. It is of course an unwieldy procedure, and while some temporary reduction in the tendency toward arcing or cold emission may be observed in some instances, the spot knocking technique fails to eliminate the cause of the trouble because extraneous particles or their combustion products remain within the envelope and constitute a source of possible future dilficulty.

It is the principal object of the present invention to provide a new and improved method of minimizing arcing in the electrode system of an electron-discharge device of the type adapted for high-voltage operation.

It is a further object of the invention to provide such a new and improved method which is convenient and inexpensive to employ in the large-scale commercial production of such devices.

In accordance with the invention as applied to the manufacture of a cathode-ray tube comprising an electrode system mounted in an evacuated envelope and adapted for high-voltage operation, the new and improved method of minimizing arcing during subsequent operation of the electrode system comprises the completing of all manufacturing and assembling operations on the electrode system which can be performed outside of the envelope, thereafter completely immersing the electrode system, initially at a predetermined ambient temperature, in a liquid medium maintained at a temperature substantially below this ambient temperature and having a boiling point intermediate the temperature of the liquid medium and the ambient temperature, to induce localized turbulence in the liquid medium at the areas of contact thereof with the electrode system, withdrawing the electrode system from the liquid medium when the turbulence has at least substantially abated and thereafter, before said electrode system reaches said ambient temperature and without further processing of the electrode system, sealing the electrode system into the envelope.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The organization and manner of operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which the single figure is a side view, partly in cross-section, showing the electron gun assembly of a television picture tube being immersed in a liquified gas in accordance with the present invention.

In accordance with the present invention, as applied to the manufacture of television picture tubes, the electron gun assembly 10 is constructed in an entirely conventional manner, including its assembly to a glass press 11 which is provided with an exhaust tubulation or stem 12. After all of the manufacturing and assembly operations which can be performed outside the envelope have been completed, the gun assembly, in the condition shown in the figure, is temporarily immersed in a liquid medium 13 maintained by means of a vacuum flask 14 or the like at a temperature substantially below the ambient temperature of the gun assembly immediately prior to immersion. Liquid medium 13, which is preferably a liquefied gas such as liquid air, liquid nitrogen or liquid oxygen, has a boiling point intermediate the temperature of the liquid medium and the initial ambient temperature of the gun assembly prior to immersion. In practice, the initial ambient temperature of the gun assembly is not critical, and no pre-heating or pie-cooling is required; immersion of the gun assembly at substantially room temperature as determined by the ambient factory conditions is preferred for convenience.

Upon immersion of the gun assembly in liquid medium 13, as shown in the figure, a localized turbulence is observed in liquid medium 13 at the areas of contact thereof with theelectrode system 10. ation is performed manually, by grasping stem 12 and suspending the electrode system in liquid medium 13, the vibrations induced by the turbulence are quite perceptible to the touch. The attendant ebullition or boiling action is readily observed visually. The turbulence is induced by localized boiling of the liquid medium v13', which takes place without the application of heat other than that introduced by immersionbf the gun:assembly at or near,

room temperature, since the boiling point or ebullition temperature of the liquid is well below room temperature. The vturbulenc;e, with attendant vibration of the electrode system, isobserved until the temperature of the gun structure 10 has dropped below the boiling point of liquid 13,

.at which time the turbulence subsides and the gun :Stl'llC- ture'lt) may be withdrawn; The entire operation may be performed manually or automatically, and requires only from to seconds.

As soon as possible after withdrawing the gun assembly from the-vacuum. flask 14, and without any further processing of the electrode system, the gun assembly 10 a If the immersion 0per-' is inserted in the neck of the picture tube envelope and press' llt'is sealed in place inan entirelyconventional i manner.- The tube is then processedto" completion in the usual way.

Liquid air, liquid nitrogen and liquid oxygen are preferred because of their chemical compatibility ;with the other components of the picture tube, and because-irn- I mersioninsuch media does'not result in the formation of foreign'deposits onthe gun parts. The ambient=tem.-

peratures of these media at atmospheric pressure are approximately equal 'to their ebullition temperaturesand are about 1-25 degreescentigrade for liquid oxygen, l50 degrees Centigrade for liquid air, and -200 degrees centigrade for liquid nitrogen, the latter being preferred as. providing the most pronounced ebullition or boiling action.

It has been discovered that the use of this simple additional procedure in the commercial-production of television picture tubeseffects a substantial reduction in the amount of arcing and cold emission encountered in the.

While accurate finished tube in subsequent operation.

measurement is difficult to achieve,it may be demonstrated that the threshold of arcing voltage is increased in this manner by at least,4 and in some instances as much as 10' kilovolts or more, thus effectively eliminating arcing;

asa cause of in-plant rejects, and eliminating the necessity for employing the spot knocking procedure. This improvement is apparently attributable to the highly effective cleaning action. provided by localized ebullition vor boiling of the liquefied gas which imparts. a substantial-E high frequency vibration to the electrode system 10 This. vibration literally shakes particles of dust, lint-or other contaminants off'the: gun structureand is possibly as sisted by quick-freezing of these contaminants which may.

render them brittle and more-easily separable from the electrode surfaces. electrode system are readily observable as a precipitate .in

The particles thus removed from the the liquid medium 13, even with gun assemblies with which the utmost care in maintaining cleanliness has been exercisedlin prior processing and handling.

It is important to seal the electrode ,system into the envelope as soon as possible after withdrawing the gun assembly from liquid medium 13, and in any event without performing any intervening processing steps; re-ex-' posure of the gun assembly to air for as much as several minutes before sealing and after withdrawal from medium 13 may permit a further accumulation of foreign particles, on the surfaces of the gun assembly, as may be demonstrated by redipping'in medium 13 andobserving the additional precipitate which is formed.

It has also been observed that, although the gun assembly as immersed in the'refrigerated liquid medium 13 5 includesa cathode sleeve which has been pre-coated as an intermediate step in the process of forming a thermionic surface, the turbulence attendant vibration of the. gun parts .is not sufiicient to substantially disturb the .coated. cathode surface.

There is nothing critical about the immersion processof liquid medium; 13 and the.

of they presentinvention, and it can be performed by an entirely unskilled operator without the provision of expen sive manufacturing equipment or production space. The

benefits of the invention are achieved with immersion for, only 5 ,or 10 seconds, although {immersion for'a longer time is; not harmfuL' Production experience has shown that it is extremely difficult with'conyentional processing. to maintain an incidence: of arcing inproduction tubes as low as v10. percent; by employing the: procedure of the present invention, the incidence of arcing is reduced to a fractionkof one percent. At the same time, a reduction in cold emission by as much as'25 to 50 percentisachieved,

While a particular embodiment of the invention has been shown and described, it will be obvious: to those.

skilled in the art that changes and modifications may be made without departing fromthe invention in its broader within the true spiritf'and scope or; the invention.

We claim:: g a l; Inthe manufacture of a cathode-ray tube compris' ing antelectrode system mounted in an-evacuatedzenve' lope and adapted for high-voltage operation, the method,

of minimizing arcin'g in said; electrode system quentzoperationswhich comprises:

completing all manufacturing and assembling opera-.

tions on said electrode system which can be formed outside said envelope; thereafter completely immersing said electrode system, initially at a predetermined ambient temperature, :in

in 'fsubsea liquid medium. maintained. at a temperature sub stantially belowsaid ambient temperature and hav V aspects, and, therefore, the aim: in'the appended claims is to cover all such changes andmQdifications as fall ing a boilingpointintermediate z=said temperatureof said liquid medium and said ambient temperature essing of said electrode system, sealing said electrode 5 system into said envelope.

turbulence has at least substan 2'. In themanufacture of a cathode-ray tube comprise" ing an electron gun'having a thermionically emissive ca't h,

ode mounted in an evacuated-"envelope andadapted fur.

high-voltage operation, thel'method. bf-minimizing arcing. in said electrode system in subsequent' operation;which' comprises: 7

providing an electron gun;.assembly,, including a cath.

ode element having a coated surface adapted to' be rendered thermionicallyj.emissive in zsubs'equentprocessing of said tube, on which all manufacturing and assembling operations which I can .be performed out side said envelopehave been completed thereafter completely immersing said electron gun as sembly, initially at-substantially'normal room tem* perature, in a liquified gas having ,aboiling point substantially below said room temperaturegwhere upon substantial'turbulence of said fgasis induced.

at the areas of contact thereof :with' saidelectron gun assembly; 7 withdrawing said electron 'fied gas when said turbulence has at least substanr tiallyabated; i r f. and. thereafter, before saidelectron; :gun assembly reaches said room temperature and.without.further assembly; fromsaid liquir,

processing thereof, :sealing said electron. gun assem-- bly into .said envelope;

5 6 3. The method of claim 2, in which said liquified gas 5. The method of claim 4, in Which said liquified gas is one of the group consisting of liquid air, liquid nitrois one of the group consisting of liquid nitrogen, liquid gen and liquid oxygen. air, and liquid oxygen.

4. The method of minimizing arcing in a cathode-ray tube which comprises subjecting the electron gun of said References Cit d by th Ex min r cathode-ray tube to ebullition in a liquified gas at a temperature substantially below normal room temperature, UNITED STATES PATENTS and sealing said electron gun into the cathode-ray tube ,364,536 12/1944 Kent 316-1 envelope before said electron gun has reached room temperature. 10 RICHARD H. EANES, JR., Primary Examiner. 

1. IN THE MANUFACTURE OF A CATHODE-RAY TUBE COMPRISING AN ELECTRODE SYSTEM MOUNTED IN AN EVACUATED ENVELOPE AND ADAPTED FOR HIGH-VOLTAGE OPERATION, THE METHOD OF MINIMIZING ARCING IN SAID ELECTRODE SYSTEM IN SUBSEQUENT OPERATION WHICH COMPRISES: COMPLETING ALL MANUFACTURING AND ASSEMBLING OPERATIONS ON SAID ELECTRODE SYSTEM WHICH CAN BE PERFORMED OUTSIDE SAID ENVELOPE; THEREAFTER COMPLETELY IMMERSING SAID ELECTRODE SYSTEM, INITIALLY AT A PREDETEMINED AMBINET TEMPERATURE, IN A LIQUID MEDIUM MAINTAINED AT A TEMPERATURE SUBSTANTIALLY BELOW SAID AMBIENT TEMPERATURE AND HAVING A BOILING POINT INTERMEDIATE SAID TEMPERATURE OF SAID LIQUID MEDIUM AND SAID AMBIENT TEMPERATURE TO INDUCE LOCALIZED TURBULENCE IN SAID LIQUID MEDIUM AT THE AREAS OF CONTACT THEREOF WITH SAID ELECTRODE SYSTEM; WITHDRAWING SAID ELECTRODE SYSTEM FROM SAID LIQUID MEDIUM WHEN SAID TURBULENCE HAS AT LEAST SUBSTANTIALLY ABATED; AND THEREAFTER, BEFORE SAID ELECTRODE SYSTEM REACHES SAID AMBIENT TEMPERATURE AND WITHOUT FURTHER PROCESSING OF SAID ELECTRODE SYSTEM, SEALING SAID ELECTRODE SYSTEM INTO SAID ENVELOPE. 